NL8702809A - PUT PROFILE DETECTOR. - Google Patents

Description

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Well profile detector.

The present invention generally relates to scintillation detectors used, for example, to measure the radiation at successive depths of boreholes in the earth and, more particularly, to a scintillation detector with improved performance and durability.

Scintillation detectors contain a scintillation crystal that emits light when hit by an ionizing particle. The crystal is surrounded by a reflector that captures and reflects the light from the crystal.

The crystal and reflector are housed in a house with a window transparent to the light produced by the crystal. The light from the crystal is then passed through the window into a photomultiplier tube and converted into an electrical signal. This process can be used to identify the type and amount of isotopes present.

The crystals used in such detectors are often metal halide crystals, such as 20 thallium-activated metal halide crystals. These metal halide crystals are known to be mostly hygroscopic and absorb water on their surfaces from the air.

As a result, a film develops on the crystal surface, which film decreases the reflectivity of the crystal walls and causes a serious decrease in light output. This decrease in light output adversely affects the performance of the crystal. To prevent this, the detectors are mounted in a dry box to reduce exposure to moisture and the scintillation crystals are typically hermetically sealed in metal containers or houses.

US Patent 4004151, which was assigned to the assignee of the present invention and is incorporated by reference herein, describes a scintillation detector of the type to which the present invention pertains. This reference describes a detector which includes a tubular sheath containing a scintilla. & / ü ï B u 0 f f - 2 - ¥ tie crystal surrounds. The tubular casing is closed by a plug or cap at one end and the crystal is spring loaded to a window at the other end to which the crystal is optically coupled. This spring loading permits thermal expansion of the crystal with respect to this casing, resulting from the higher thermal expansion coefficient of the crystal with respect to the casing material. In addition, this patent describes in detail the types of scintillation crystals used in such devices, their operation and requirements.

US Patent 4158773, which was also assigned to the assignee of the present invention and is incorporated herein in its entirety, describes a scintillation detector with a special light transfer and reflector means consisting of a soft, elastic, silicone, rubber canister improving the shock absorption for protecting the crystal, increasing the light reflection of the crystal.

US Patent 4383175, also assigned to the assignee of the present invention and incorporated herein in its entirety, again describes a similar scintillation detector having an improved hermetically sealed housing and window assembly to reduce the exposure of the crystals to moisture.

25 One of the main applications of scintillation detectors is in the oil well industry. In addition, the detectors are lowered into the borehole along with other instruments to collect geological data from the bedrock layers to determine whether the well will be an effective producer. This process is commonly known as well profiling. As it travels down the borehole, the instrument package can be exposed to shock loads as high as 100 to 150 g and temperatures as high as 200 ° C. Therefore, the crystals are mounted in the containers with special shock absorbing techniques to prevent damage to the crystal.

The present invention has identified and addressed the major problems encountered in this application of the detectors. These problems exist. 8 7 0 1 & 0 9 - 3 -, '! This means that the high shock and vibration loads will result in the reflective media shifting in the detector, and subsequent prolonged exposure of the detector to temperatures in the range of 150 to 250 ° C will result in a brown film develops on the crystal surface. This impairs the detector performance. It is believed that one reason why these problems are not understood is that the scintillation detectors are so inaccessible during use and it has been easy to be generally blamed for the reduced performance due to mechanical and thermal failures that occur during installation and use.

The crystal for recording the oil well profile is typically a long, narrow configuration connected to the exit window at one end of the housing. The window is linked to the photo tube. The performance of this configuration is highly dependent on uniform light production over its entire length. Shifting of the powder reflectors, due to excessive vibration, disturbs the light balance and results in reduced performance.

In order to solve this problem, Teflon tape, a high temperature plastic with good reflective properties, has been tested as a reflector. This material provides a very efficient stationary reflector, which allows thermal expansion of the crystal and does not shift under shock and vibration. A drawback of the tape, however, is that the temperature deterioration is enhanced in the long term and the light output can drop by as much as 60%.

The present invention prevents the deterioration of the ring that occurs with both powder reflectors and Teflon tape.

The present invention is directed to new and improved scintillation detectors. The invention also relates to an improved method of manufacturing scintillation detectors.

According to the invention, a hermetically sealed housing surrounds an elongated scintillation crystal in an atmosphere of non-reactive gas. This provides increased detector life.

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The housing is illustrated as a stainless steel tube with a translucent window on one end. The window is held in a window assembly that closes the window into the housing.

5 The scintillation crystals work by converting the energy of the ionizing particles of gamma rays into light energy. Types of crystals that are effective include alkali metal halide crystals activated by inclusion of thallium, cesium halide crystals, bismuth gum-10nate; and plastic scintillators.

Since the performance of the crystal depends on how efficiently the produced light can be received, the crystal is surrounded by a reflector for light in the 300 nm to 500 nm wavelength range. In addition, this reflector contributes to insulating the crystal from shocks.

Thus, it is desirable to use reflective powders of metal oxides such as or MgO as the reflector. Polytetrafluoroethylene tape (known under the DuPont trademark "Teflon") wrapped around the crystal surface is also effective.

The crystal, surrounded by the reflector shock absorber, is sealed inside the housing in an atmosphere which substantially reduces the exposure of the crystal to moisture and reactive gases such as oxygen. In one embodiment of the invention, the crystal is contained in an atmosphere of a non-reactive gas, such as nitrogen, CC 2, or one of the noble gases.

The invention also relates to methods of manufacturing the detector. In a first embodiment, the crystal is contained in a non-reactive atmosphere in the house. Such encapsulation can be accomplished by assembling the flushed components in a work box filled with the non-reactive gas.

In another embodiment, the detector is formed by assembling the detector and then evacuating the housing and using a non-reactive gas to refill the housing. Alternatively, in this embodiment, after assembly, the atmosphere in the detector is purged with a non-reactive gas.

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These techniques allow the manufacture of well profile detectors that are both temperature stable and insensitive to changes from the reflector sliding in the container.

These and other aspects of the present invention are more fully described in the following description and drawing, in which: Figure 1 is a longitudinal cross-sectional view of an assembled scintillation detector according to the present invention, showing a first embodiment of the invention wherein the reflective medium is a reflective powder.

Fig. 2 is a longitudinal cross-sectional view of an assembled scintillation detector according to the present invention, showing a second embodiment of the invention using a layer of Teflon as the reflective medium.

Fig. 1 shows a typical scintillation detector according to the present invention. The detector includes a tube-20 shaped, stainless steel housing 10 containing a cylindrical scintillation crystal 11.

The crystal may consist of an alkali metal halide activated by the inclusion of thallium, sodium, or rare earths, such as Nal (Tl), KBr (Tl), KI (T1), and KCl (Tl); Csi (Tl) and CsI (Na); and Lil (Eu) bismuth germanate; or a plastic scintillator, such as NE102 polyvinyltoluene plastic. Plastic scintillators are molecular crystals in which the intermolecular bond is very weak compared to the ion crystal bond and in which the photo-luminescence occurs from the excitation of the first excited electronic state. Molecules that have a high resonance energy, such as unsaturated cyclic molecules and more particularly, benzene or benzene derivatives, exhibit excellent organic scintillation properties. A plastic scintillator can consist of one or more fluorescent organic compounds dissolved in a solid plastic bases. Some examples of the fluorescent compounds include, but are not limited to, POPOP, tetraphenylbutadiene, butyl PBD, and naphthalene. Examples of the 87 0 2 J 0 9 * -6-t plastics materials are polyvinyltoluene, polystyrene, poly-methyl methacrylate, polyethyl methacrylate, and copolymers thereof. These plastics may also contain cross-linking additives such as, but not limited to, divinyl benzene.

5 U.S. Patent 3,960,756 to. Noakes, transferred to the same entitled party, discusses organic scintillation matrices and is incorporated herein by reference.

The housing 10 consists of a tubular metal 10 body 12 which is closed at one end by a window assembly 13 and at the other end by a metal plug or cap 14. Both the window assembly 13 and the plug 14 are soldered shut at the respective ends of the body 12 by peripheral welds at 17 and 18, respectively.

The crystal 11 is cut or machined to yield a right angle cylinder which has a smooth, cylindrical external surface 21 and flat and parallel end surfaces 22 and 23. The end face 22 is adjacent to the window assembly 13 and a spring system 24 is mounted between the end cap or plug 14 and the other end face 23 to resiliently push the crystal 11 toward the window assembly 13. This maintains optical coupling through a layer of a suitable optical coupling material 26 between the crystal 11 and the window assembly 13. 25 Placed between the spring system 24 and the end face 23 of the crystal 11 is a back plate 27 formed of a scintillating light-reflecting material. In the illustrated embodiment, the spring system includes several wave-shaped springs and spacer plates. However, other types of suspension systems can also be used if desired.

The window assembly 13 is formed from a cylindrical piece of glass 31 hermetically sealed in a window retaining ring 32. The glass material is transparent to the type of light emanating from the respective scintillation crystal 11 when such a crystal is bombarded by ionizing radiation.

An example of a type of glass that can be used in the window assembly 13 is a soda lime glass with a thermal expansion coefficient at room temperature of

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- 7 - “6 o approx. 8 x 10 to 10x10 cm per cm per ° c. For example, the ring 32 may be a stainless steel ring with a thermal expansion coefficient of about 9 x 10 to 12 x 10 cm per cm per ° C. For a particular assembly, when a pressure seal is desired, the ring 32 is selected to have a slightly greater thermal expansion coefficient than the glass 31, and this differential thermal expansion is used to effect a pressure seal. on the contact surface 33 between the glass 31 and the ring 10 32.

The pressure seal alone can be used to provide hermetic seal as required. For example, when the ring is formed of a nickel-plated, cold-fanned steel, the glass does not provide a significant chemical bond with the nickel cover material. However, when the thermal expansion coefficients are related, for example, as set forth above, and the cooling is suitably controlled, the ring is under tension and the glass is pressurized to form a pressure seal therebetween.

The pressure seal can be accomplished by heating the glass 31 and the ring 32 above the glass processing temperature so that the glass flows in contact with the ring, as described in U.S. Patent 4383175, assigned to the assignee of present application. This literature reference, which has previously been incorporated herein by reference, also describes structures and methods for attaching the window assembly 13 to the tubular body 12 which involve fusing the metal tubular body 12, the ring 32 and the cap 14. Similar methods can be used to close the cap 14 at the other end of the tubular body 12.

After the cooling is complete, the glass is dragged and polished, as required, to provide the desired scintillation, light transmission properties.

Placed around the outer surface 21 of the crystal 11 is a reflective medium 28 that performs two functions. Its primary function is to reflect 8 / D l, ü ü * - 8 - light and improve detector performance by improving the capture of the light produced by the crystal. A secondary function of the reflective medium 28 is to help protect the crystal 5 from high shock loads that the detector may experience during use. In the first embodiment of the present invention, the reflecting medium 28 is a light-reflecting powder, for example, metal oxides such as A12C> 3 or MgO. The powder is packed between the crystal 11 and the tubular housing 12. A lubricating layer, such as a split sheet of Teflon, may be applied between the crystal surface 21 and the reflective medium 28 in order to apply the loading forces on the crystal 11 due to the difference in thermal expansion coefficients.

At each end of the crystal 11, an O-ring 29, 30 is arranged around the crystal 11. These O-rings maintain the centering of the crystal 11 and enclose the powder packing along the length of the crystal so as to form the powder keep in contact with the crystal surface. In this way, the powder is retained as almost a solid can.

In an alternative embodiment of the invention, shown in Fig. 2, the reflecting medium 128 is polytetrafluoroethylene ("Teflon"), such as one or more layers of Teflon tape. The tape is wrapped around the curved crystal surfaces so that the tape edges overlap. In the fig.

2, the crystal 11 is wrapped with tape so that three layers 135 of Teflon are formed. 0.0025 cm layer of aluminum foil 136 covers it and is eventually covered by another single layer 137 of Teflon tape. An additional 30 layer of shock absorbing material 150 such as a potting mixture or powder may be used in this embodiment to assist in protecting the crystal from impact and to provide additional support. The flat end surface 123 can also be wrapped. The flat end surface 122 is not wrapped to allow light metering through the window 131.

The crystal is sealed in the tubular housing in a substantially non-reactive atmosphere. In the past, it was not known that the atmosphere in the house would affect the performance. 8/0 * 1 I · V ·% é v - 9 - could affect scintillation detector life and the crystals were sealed in air.

The problems associated with the use of an air atmosphere become apparent, especially after the detector is lowered into the borehole. While it was previously known that detector performance may deteriorate in situ, an understanding of these problems has now been developed and supported by the following evidence. During the descent process and while the detector is in place, it can be subject to high shock loads and temperatures. These conditions apparently cause changes in the reflective packing layer 28, leading to deterioration of the crystal. When reflective powders are used, the high shock and vibration loads cause the reflective powder to shift. As a result, over time, the prolonged exposure of the crystal to an oxygen-containing atmosphere in a closed container, at these elevated temperatures from 100 ° C to 200 ° C, results in a brown film developing on the crystal surface. This film degrades the efficiency of the reflective medium surrounding the crystal.

The scintillation detector crystal 11 is a long, narrow, right angle cylinder optically coupled with one end to a photomultiplier. Uniform light production over the entire length of the crystal is necessary to ensure the proper functioning of the crystal. Shifting the reflective medium disturbs the light production balance and causes deterioration. This problem is exacerbated where the crystal surface 21 has an increased exposure to an oxygen atmosphere and the light-inhibiting film develops on the crystal surface. This deterioration of the detector, which has a powder reflecting medium and an air atmosphere, was found to decrease the light output between 10% and 20%.

It was believed that the deterioration problems were largely due to the shifting of the reflective powder medium 28. One solution to this problem was to add the O-rings 29, 30 to contribute in è / Ü C vw 5-10 - the holding the powder in the correct position in contact with the crystal surface 21. A further attempt to solve this problem was to replace the reflective medium 28 with Teflon tape (as shown in Fig. 2). Teflon 5 was chosen because it is a high temperature plastic with good reflective properties. Other plastics with similar properties can be substituted. It was believed that the Teflon would be soft enough to allow the crystal expansion and not shift with shock and vibration. However, the replacement of the Teflon tape for the powder reflective medium did not solve the deterioration problem since the long term temperature deterioration was enhanced. The light output decreased as much as 60%. It is believed that the tape confines the film to the crystal surface and that other solids, such as aluminum foil or a reflective sleeve, would act in the same manner.

These problems are solved by the present invention by incorporating the crystal 11 in an unreactive gas. Examples of suitable gases are nitrogen, carbon dioxide and argon, although any inert or relatively unreactive atmosphere will also work. As used in this application, a non-reactive atmosphere is understood to be an atmosphere that contains no reactive oxygen or is substantially depleted in oxygen.

Several methods can be used to obtain the desired result. The following examples illustrate the present invention: the crystal 11 can be encapsulated with a non-reactive gas or housing 10 can be evacuated after encapsulation and refilled with a non-reactive gas. Alternatively, the housing 10 can be flushed after encapsulation, until all reactive gases have been replaced with the non-reactive gas.

In order to accomplish encapsulation with a non-reactive gas, the detector can be assembled in a work box containing the non-reactive atmosphere. The purified components of the detector are placed in the and cabinet flushed with a suitable gas, such as argon. The components v, w> - 11 - components are then assembled in the work box containing the argon atmosphere. The house 11 is then closed.

Alternatively, the detector can be assembled to form a sealed unit, as known, but the atmosphere in the house can then be evacuated and the house refilled with a non-reactive gas. Also, the sealed unit can be purified from the reactive gas, such as by purging with a non-reactive gas. When the gas overflow from the housing is non-reactive and stable in composition (i.e. relatively pure non-reactive gas), the housing can be closed.

EXAMPLE X

15 Effect of argon on G-style temperature deterioration

Four detectors were built with Teflon tape, two of which were assembled using current standard practice, while the other two were built in an argon atmosphere.

Preparation:

A dry box was used to assemble the detector. This cabinet consists of a container which forms a closed environment which is accessible through closed access openings equipped with gloves in order to allow the assembly of the materials. The dry box was opened and thoroughly cleaned. The detector hardware was cleaned by the standard shake and bake method. The scintillation crystals were brought into contact with the glass in the dry box.

All hardware,. packaging materials and reflector materials were then transferred to the clean splice case. For the two argon detectors, the dew point of the argon cylinder was measured at -55 ° C on the automatic dew point meter.

The argon cylinder was then connected to the splice case and the case was flushed with argon until a dew point of -55 ° C was obtained with the dew point meter.

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The crystal surfaces were prepared with be. 87 0 2; ' C ï - 12 - help from standard air or argon atmosphere.

The crystals were wrapped with three wraps of Teflon tape, then with a layer of 0.0025 cm aluminum foil and a fourth wrap of Teflon tape. The crystals 5 were then welded in these houses in dehydrated air or the argon atmosphere.

Test method;

A 5.1 cm standard tube was used to measure the pulse height and resolution. The 2.86 cm x 2.86 cm stan-10 standard crystal was set to channel 1000 on the standard tube. The electronic pulsator was also set to channel 1000. The four 3.8 cm x 10.2 cm crystals were measured with respect to pulse height and pulse height resolution before and after repeated heating cycles to 160 ° C with a four hour pass at temperature. The results and data are stated below:

Data interpretation:

The performance of a scintillation crystal can be determined with respect to the brightness of the light emitted as a result of the single gamma ray collision. The light being recorded has a Gaussian distribution where the height of the curve is called the pulse height or peak channel and the width of the curve is called the resonance. A sharper resonance gives a more clear pulse resolution and greater pulse height.

For scintillation crystals, these measurements were taken twice, once with the source orientation parallel to the long axis of the crystal, known as "end on" measurement, and once with the source orientation transverse to the long axis of the crystal, known as "broad beam "measurement. Ideally, when the crystal is in balance, these two measurements should approximate each other.

The results are set out below. "P.H." gives the pulse height and "Res." represents the resonance.

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Analysis:

After two, four-hour cycles at 160 ° C, the two Argon-filled detectors decreased in pulse height by an average of 2.2%, while the two air-filled samples decreased by 8.4% on average. After two, four-hour cycles at 180 ° C, the two Argon-filled detectors lost an additional 2.2% pulse height, while the air-filled specimens lost an additional 14.4%. After two, four-hour cycles at 200 ° C, the Argon-filled specimens showed a total loss of 6.8% pulse height for all cycles, while the total loss in pulse height for the air-filled specimens was 40.7%.

These tests demonstrate that replacing a non-reactive gas for air with the detector house assembly substantially increases the detector's performance and performance time. The effect of the invention appears to be more dramatic as the temperature to which the detector is exposed increases and the duration of exposure to the adverse conditions increases.

Initially, it would not be obvious that a non-reactive atmosphere would be preferable to air, since the benefit only becomes apparent when exposed to elevated temperature for an extended period of time. The pulse height of the crystal, when enclosed in argon, is lower than air before the unit has been exposed to heating for extended periods of time.

EXAMPLE II

Test method;

Tests were performed using the preparation assembly techniques and test techniques similar to that of Example 1. For this example, detector performance was tested for the crystals of specified size and for crystals manufactured as described in the tables. The pulse height was measured at time zero> 35 after 24 hours at 185 ° C, and after 12 hours at 200 ° C. The change in pulse height was recorded as a percentage change from the starting figure.

Analysis:

Again, a significant improvement was demonstrated

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- 17 - in the pulse height level maintained for detectors with non-reactive atmospheres. An additional pulse height measurement of the first test samples after 24 hours at 200 ° C showed no significant change of the samples after 12 hours (i.e. 12.6% and 12.5%, respectively). This example illustrates that an inert gas, such as argon, is the preferred atmosphere - that detectors with a non-reactive atmosphere such as nitrogen and CC 2 atmospheres perform better than detectors with air atmospheres.

10 "T.T." indicates Teflon tape as a reflective medium.

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EXAMPLE III

Effect of nitrogen on temperature deterioration

Four detectors, each measuring 3.8 cm x 10.2 cm crystals, were assembled with Teflonta reflectors. Two were formulated using current standard practice and the other two were formulated in a nitrogen atmosphere.

Preparation;

A dry box as described in Example I was used to assemble the detector. The dry box was opened and thoroughly cleaned. The hardware was cleaned by the standard shake and bake method. The crystals were combined with the glass in the dry box. All hardware, packaging materials and reflector materials were then placed in the clean splice case. The dew point of the nitrogen cylinder was measured at -55 ° C with the automatic dew point meter. The nitrogen cylinder was then connected to the splice case and the case purged with nitrogen until a dew point of -55 ° C was obtained with the dew point meter. this took two hours.

Assembly:

The crystal surfaces were prepared using standard nitrogen atmosphere practice. The crystals were wrapped with three wraps of Teflon tape, then a layer of 0.0025 cm aluminum foil and a fourth wrap of Teflon tape. The crystals were then welded in these houses in the nitrogen atmosphere.

Test method:

A 5.1 cm standard tube was used to measure the pulse height and resolution. The 2.86 cmx 2.86 cm standard crystal was set to channel 1000 on the standard tube. The electronic pulsator was also set to channel 1000. The 3.8 cm x 10.2 cm crystal was measured with respect to the pulse height and pulse height resolution before 35 and after repeated heating cycles at 160 ° C with a four hour soaking at the temperature. The results and data are listed below.

Analysis:

The pulse height change for the nitrogen samples 40 was not as good as observed for the argon samples. 8 7 i i: - 20 - but the changes were relatively stable and amounted to about half the rate of change observed for samples trapped in air and subject to the same conditions. This shows that nitrogen is also a suitable non-reactive gas that works in the present invention.

For cycle

End On Broad Beam 10 ____________________________ P. Hi / Res ___________ P JWRes______ nitrogen 1 860 7.1 867 7.0 nitrogen 2 888 6.9 886 7.0 160 ° C after 15 4 hours________________________________________________________

End On Pulse Height Broad Beam Pulse Height _____ P ^ EL / Res __ change ___ P ^ H ^ / Res s __ change __ nitrogen 1 831 7.3% -29 3.4% 839 7.2% -28 3.2% nitrogen 2 853 7.1% -35 3.9% 849 7.3% -37 4.2% 20 standard 1008 +8, 8% pulsator test 1003 160 ° C after 5 | _hour ______________ 22 End Ch pulse height Broad Beam pulse height __________ P ^ H ^ / Res__ change ___ P-H ^ / Res ____ change____ nitrogen 1 819 7.4% -41 4.8% 828 7.0% -39 4.5% nitrogen 2 839 7.1% -49 5.5% 833 7.3% -53 6.0 % standard 1005 +5.5% pulsator 1001 30 180 C after 4 hours_____________

End On pulse height Broad Beam pulse height __________ P ^ iL · / Res s__ change ing ___ P ^ H ^ / Res ____ change ing____ nitrogen 1 807 7.3% -53 6.2% 815 7.1% -52 6.0% 35 nitrogen 2 820 7, 2% -68 7.7% 814 7.4% -72 8.1% standard 996 -4.4% pulsator 1000 rf \ "» ti <! V t. - - 21 - »<180 ° C after 4 hours______________________________________

End On Pulse Height Broad Beam Pulse Height __________ P ^ H ^ / Res__ Change ___ Change 5 Nitrogen 1 805 7.3% -55 6.4% 810 7.2% -57 6.6% Nitrogen 2 804 7.3% -84 9.5% 800 7.5% -86 9.7% standard 1010 +10 1.0% pulsator 1000 10 200 ° C after 4 hours__________________________________________ _____

End On Pulse Height Broad Beam Pulse Height __________ P ^ H ^ Res Change ___ P ^ H ^ / Res ____ Change____ Nitrogen 1 785 7.5% -75 8.7% 792 7.1% -75 8.7% 15 Nitrogen 2 779 7.3% - 109 12.3% 771 7.8% -115 13.0% standard 1000 +0 0% pulsator 1000

200 ° C after 4 hours

20 2θ_ογο1υΞ ____________________________

End On pulse height Broad Beam pulse height __________ P ^ H ^ / Res change PJH ^ / Res ____ change____ nitrogen 1 774 7.3% -86 10% 776 7.3% -91 10.5% nitrogen 2 753 7.4% -135 15, 2% 746 8.0% -140 15.8% 25 standard 991 -9, 9% pulsator 999

EXAMPLE IV

Effect of vacuum on temperature degradation A 3.8 cmx 15.2 cm housing was constructed with 30 threaded ends and O-ring seals.

A copper tube was soldered into the back of the house to allow for evacuation.

A 3.8 cm x 15.2 cm crystal was brought together with the window of this container. The crystal was completely sanded in the dry box and sealed in the container. No reflector was used. All hardware was cleaned and leak-treated with the helium leak tester prior to assembly. The detector was then tested for leakage. At this time, the leak tester indicated that. 87 0 2 L w 9 * - 22 - there may have been some minor leakage, but its location could not be accurately determined. The detector was then placed in an oven and connected to the research oven vacuum system. The detector was then evacuated to less than 1 micron and pumped overnight. The oven was heated to 215 ° C for 16 hours while the vacuum system continued pumping the detector. Pulse height and resolution measurements were made before and after the baking cycle.

(See data). The detector was then sealed and baked again at 215 ° C for 16 hours. The pulse height and resolution were again measured. (See data).

During the closed baking operation, the vacuum gauge rose to 500 microns, indicating that a small leak was present.

At this point, the crystal was removed from the container because a substantial decrease in yield had occurred. There was no indication of surface hydration at this time. The crystal was then wrapped in Teflon tape, and it became clear that a brown discoloration was present on the crystal surface.

Pulse height measurements were made using the standard 2.86 cm x 2.86 cm crystal for comparison.

Analysis: The vacuum samples were again not as favorable as the argon samples. It is possible that at least part of the results can be attributed to the leak found. However, extrapolation showed results to be better than air samples for the same conditions.

While the invention has been explained and described with respect to a special embodiment thereof, the latter is for purposes of illustration and not limitation, and other variations and modifications of the specific embodiment shown and described herein will be apparent to those skilled in the art all are within the intended scope and scope of the invention. Accordingly, the invention is not limited in scope and operation to the special embodiment described and shown herein, or in any other manner inconsistent with .8702.

The extent to which advancement in the art has been promoted by the invention.

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Claims (19)

1. Scintillation detector characterized by a scintillation element capable of converting the energy of an ionizing particle into light generator 5? a housing encapsulating the scintillation element, the housing comprising a light transmitting means optically coupled to the scintillation element; sealing means hermetically sealing the housing; and an atmosphere that is substantially non-reactive to the scintillation element in the house. 2. Scintillation detector according to claim 1, further characterized by a reflector element in the housing which receives and reflects light from the scintillation element. Scintillation detector according to claim 2, verr. characterized by shock-absorbing elements which have the function of protecting the scintillation element from externally applied forces. 4. Scintillation detector according to claim 1, characterized in that the scintillation element consists of an element of the group comprising alkali metal halide crystals, cesium halide crystals, bismuth germanate, and plastic scintillation compositions. Scintillation detector according to claim 1, characterized in that the scintillation element consists of an element from the group of Nal (Tl), NaBr (Tl), KBr (Tl), KI (Tl), KCl (Tl), CsI (Tl), CsI (Na), or polyvinyltoluene plastic scintillators. 6. Scintillation detector according to claim 1, characterized in that the atmosphere consists of one or more of the group helium, argon, nitrogen, carbon dioxide and a vacuum. 7. Scintillation detector according to claim 1, characterized in that the atmosphere is a noble gas. 8. Scintillation detector according to claim 3, m e t. 87 C i 3 v 9 - 26 - fc characterized in that the reflector element and the shock absorbing element consist of a reflecting metal powder which is arranged in the housing around the scintillation element. 9. Scintillation detector according to claim 2, characterized in that the reflector element comprises polytetrafluoroethylene. 10. Scintillation detector characterized by: an elongated scintillation element with longitudinal external surfaces, the scintillation element consisting of an alkali metal halide crystal; a housing that encapsulates the scintillation element and includes a light transmissive window optically coupled to the scintillation element, and a shock absorbing element that has the function of protecting the scintillation element from externally applied forces; reflector element which interacts with substantially all of the longitudinal external surfaces of the scintillation element and reflects light with a wavelength from about 300 nm to about 500 nm; 20 sealing element hermetically sealing the housing; and an atmosphere in the house that is substantially non-reactive to the scintillation element at temperatures from about 150 ° C to about 200 ° C. Scintillation detector according to claim 10, characterized in that the reflector element and the shock-absorbing element consist of a reflective powdered metal. 12. Scintillation detector according to claim 10, 30. characterized in that the reflector element consists of a polytetrafluoroethylene layer. 13. A method of manufacturing a scintillation detector with components comprising a scintillation element, a housing, and housing sealing means, including by placing the scintillation element in the housing; providing an atmosphere in the house that is substantially non-reactive to the scintillation element at temperatures of from about 150 ° C to about 200 ° C; assembling the housing and the housing sealing means to hermetically seal the scintillation element in the housing. 14. A method of manufacturing a scintillation detector according to claim 13, characterized in that the steps are performed sequentially. 15. A method of manufacturing a scintillation detector according to claim 14, characterized by an initial step of flushing out the components of gases reactive with the scintillation element. A method of manufacturing a scintillation detector according to claim 14, characterized in that all steps are performed in a closed system with an atmosphere that is essentially non-reactive with respect to the scintillation element at temperatures from approx. 150 ° C to approx. 200 ° C. Method of manufacturing a scintillation detector according to claim 13, characterized in that the housing assembly step is carried out prior to the atmosphere providing step. Method for the manufacture of a scintillation detector according to claim 13, characterized in that the scintillation element is an alkali halide crystal and the essentially non-reactive atmosphere is selected from the group consisting of the noble gases, nitrogen and carbon dioxide. A method of manufacturing a scintillation detector according to claim 13, characterized in that the substantially non-reactive atmosphere is a vacuum. . 8 7 0 £ \